Anyone else had grief with a Victron MultiPlus humming on shore power?

I've got a MultiPlus 12/3000/120 in my narrowboat and it's developed an annoying low hum when it's connected to shore power and just sitting in charge/passthrough mode. Doesn't matter whether the batteries are full or still charging — the hum is constant. It's not earsplitting but in a quiet boat at night it drives you mad. Measured it with my phone and it's roughly 50–60 Hz, so clearly mains-related somehow.

I've already tried tightening all the DC connections and checking the earth, and I swapped out the shore power lead thinking it might be a dodgy connection somewhere. No change. The unit is about 18 months old and mounted on a ply board with rubber grommets between the inverter and the board. Someone on another forum mentioned transformer hum being worse with certain grid supplies that have DC offset — apparently some marinas have grubby power that causes this?

Has anyone actually fixed this rather than just learned to live with it? Wondering whether a DC offset blocker is worth trying, or if Victron would even look at it under warranty at this age. Any experience with getting a dealer involved appreciated.

@GoldenBodger — worth checking your shore power supply quality first. Narrowboat marina supplies are notoriously dirty; I've seen THD figures of 8–12% on some pontoon pedestals which will cause the MultiPlus transformer to audibly resonate.

A few things to investigate:

• Charger current setting — back it off in VictronConnect. Full 120A charging creates more core flux, more hum.
• PowerControl/PowerAssist thresholds — misconfigured input current limit can cause the unit to hunt between modes.
• Physical mounting — rubber anti-vibration feet make a measurable difference; hard-mounted to a wooden bulkhead will amplify everything.

On my boat the hum was traced to a loose transformer lamination stack — audible only above ~80% charge current. Victron replaced it under warranty without argument, so if it's genuinely mechanical rather than electrical, raise a ticket through your dealer.

What firmware version are you running?

@GoldenBodger had this exact issue with my cabin setup. Turned out to be the transformer core vibrating — totally normal on MultiPlus units but can get worse over time or if the unit isn't mounted solid.

Few things worth checking:

• Mounting — even slightly loose bolts let the casing resonate like mad
• Input voltage — if your shore power is a bit low or dirty, the unit works harder and hums more
• Anti-vibration pads under the unit help a lot

Mine sorted itself after I re-mounted it properly on a wooden panel with some rubber washers. Night and day difference.

If it's a recent change rather than always been there, worth checking your shore power supply — some marina pedestals are genuinely awful for clean voltage.

@GoldenBodger — one thing nobody's mentioned yet: check whether the unit is rigidly mounted to a wooden panel or bulkhead. On a narrowboat especially, any slight flex in the mounting surface can act as a sounding board and amplify transformer vibration considerably. Try slipping some rubber anti-vibration mounts between the MultiPlus and whatever it's fixed to — even a few quid's worth of rubber grommets from a hardware shop can make a surprising difference. Also worth tightening all the mounting bolts first, as loose fixings make it worse. If the hum changes pitch when loads come on or off, that's a separate clue pointing more toward @RiverRunner's point about supply quality. What's your shore power pedestal — is it a proper marina hookup or a domestic socket on a long extension?

Hey @GoldenBodger — worth checking your input voltage as well. If the shore power is sitting at the lower end (say 220-222V rather than a solid 230V), the MultiPlus can work harder in passthrough and that transformer hum becomes more pronounced. I had something similar on my setup and found the marina supply was drooping noticeably during peak hours — evenings especially when everyone's got their electric heaters cranked up.

You can monitor incoming voltage through VictronConnect or if you've got a Color Control/Cerbo you'll see it logged over time. Might give you a clue whether it's worse at certain times of day. If the voltage is consistently low, worth having a word with the marina about it — some of them have genuinely poor infrastructure.

Also double-check your shore power lead and connections — a slightly loose or corroded connection can introduce resistance and make things worse.

Mine hummed like a choir on a narrowboat for months until I realised it was sitting on a metal bracket that was basically acting as a resonance amplifier — swapped it for some rubber anti-vibration mounts off Amazon and now it's quieter than my bank account.

Hey @GoldenBodger — just to add to what others have said, have you checked the transformer torque screws on the unit itself? There are usually a couple of bolts that secure the transformer internally, and they can work loose over time, especially on a boat with all that vibration from the engine and water movement. Victron actually mention this in their documentation — you can carefully re-torque them if you're comfortable opening the unit (mind the warranty situation though). Also worth checking whether the hum changes pitch when your battery bank reaches absorption or float — if it does, that points more towards the transformer magnetising at different charge currents rather than a mounting issue. Good luck tracking it down, these things can be maddening!

Great thread, this. @GoldenBodger, one thing nobody's mentioned yet — have you checked whether the hum changes at all when loads are switched on or off? If it quietens down once there's actually something drawing current, that can point toward the unit being in a sort of "idle absorption" state where the transformer isn't working particularly hard and can resonate more noticeably. Also worth having a look in VictronConnect at your charge current settings — winding it back slightly sometimes helps. Narrowboats can be tricky because shore power quality at marinas is often a bit ropey to begin with.

Hey @GoldenBodger — worth checking what your shore power supply actually looks like on an oscilloscope or even a decent clamp meter with waveform display. Marina shore power can be surprisingly grotty, lots of harmonics and distortion depending on what else is plugged in along the pontoon. A heavily distorted sine wave will make the MultiPlus transformer work harder and sing more. I had similar on a site hookup and the hum was noticeably worse when the bloke two pitches down had his cheap inverter-generator running. Might not be your unit at all — could be what's coming in. 🔌

Great points from everyone here. @GoldenBodger one thing I'd add — have you tried adjusting the shore power input current limit in VictronConnect? I've seen MultiPluses hum noticeably when they're pulling near their maximum input current, almost like the transformer's working harder than it fancies. Dropping the input limit down a notch or two sometimes sorts it right out. Also worth checking whether the hum is actually coming from the unit itself or possibly resonating through whatever surface it's mounted on — a bit of anti-vibration matting under the MultiPlus can make a surprising difference on a boat hull.

Good thread. @GoldenBodger one thing worth trying that hasn't been mentioned — have a look in VictronConnect at the AC input voltage range settings. If your shore power is sitting near the edge of the accepted range, the MultiPlus can work harder to compensate and that can contribute to audible hum. Marina shore power is notoriously variable, especially older pedestals. Also, is the unit mounted directly onto a wooden bulkhead? Resonance through the hull structure can amplify what should be a barely noticeable transformer hum into something properly irritating. Some rubber anti-vibration mounts can work wonders there.

Had this exact issue on my narrowboat setup last year. Turned out the MultiPlus transformer hums more noticeably when the AC input voltage is on the high side — marina shore power can drift well above 240V sometimes. Worth checking what voltage you're actually getting at the inlet. Mine was sitting around 248V and winding the AC input voltage limit down slightly in VEConfigure made a noticeable difference. Also make sure your MultiPlus is properly earthed and mounted rigidly — any loose bolts on the mounting panel will resonate and amplify that transformer noise considerably.