Converter hum

Most electronic device "hum" is typically from a dirty/unlubed fan or from a transformer and it's separate plates.
Solutions: Clean fan blades and housing, lube fan with machine oil on bearing underneath shaft-located sticker (I typically just tape or glue the sticker back on).
If the transformer is mounted on four corner bolts, tightening the mounting bolts can reduce hum. Likewise, tightening any bolts that hold the transformer plates together and reinforcing with varnish may reduce/eliminate hum.
Beyond that, tightening all mounting bolts and, sometimes, adding a mass deadening mat can work.
Good luck with a fix.
BTW, ascertain that it is indeed the converter and not a buzzing breaker. That can lead a guy off course.

Is it a cooling fan running?

Might just be the cooling fan.... like beemerphile1 posted. Were your batteries low? Is this the first time you have run it in a long while...It might just be working hard to charge up the batteries and run other stuff also....

Give it a day or so to get "caught up."

Dynamo hum......

Mine was running about 48 hours straight.. knew they run a lot, especially in the evening with lights on, but this was extreme. Checked battery and it was hot to the touch, pulled the caps off, and it was smoking out from all 6 holes. End of battery. Shut off electric, got new battery. End of continuous running. Above suggestions all good, too. I was never told to clean or lube anything in the converter area. Learned the hard way.

It's probably just the fan, it will get louder the more lights (load) you turn on. Perfectly normal.

The more discharged the batteries are, the louder it may hum.

Lots of things electronic (especially devices with transformers in them) Hum, because they don't know the words.

That's the line those of us that worked at Heart Interface tech support would tell people when they call and wanted to know why their inverter hummed. It ALWAYS got a good laugh from the custeemr.

SidecarFlip wrote:
Dynamo hum......

hehe Mr. Zappa I presume

These new converters make a noise sometimes it sounds like a hum but they can make other sounds that reck your piece and quiet. Long about 1998 some genius thought up a way to make the converters cheaper by adding electronics which needs to be cooled, the old ones got warm but no fan was ever needed. So much for that. I also find that noise unpleasant and called the TT Manufacturer they just act dumb like your the only one that has complained about this and you should just learn to live with it. I'm changing my lights inside over to led's to reduce the power draw and put less demand on the converter that should help but the hum will always be there unless you buy a old
TT.

travelnman wrote:
I'm changing my lights inside over to led's to reduce the power draw and put less demand on the converter that should help but the hum will always be there unless you buy a old
TT.

My converter doesn't run the fan nearly as much after I swapped in these LEDs years ago: 1141 LED