I’m working on a 6020W tender and note that the whistle relay hums when it’s under power; reminiscent of an e-unit hum. It appears to be wired correctly, but I’ve never had a whistle tender that had a noisy whistle relay. Is this normal or is there something wrong here? Thanks.
Some of them hum.
All of my whistle tenders growl when I try to use them on a low voltage and many of them hum. I would not be concerned, unless they hum when you are not trying to activate them[*-)]. In that case, you may want to get them checked out.
Some of them hum when power is applied to the track, when the whistle button is NOT pressed. It’s normal.
Thanks, everyone. I feel better now. 
as long as it doesn’t rattle & Hum [:D]