transformer hum

[mkstylee]

Hi all anyone know why my 4100 makes a loud transformer hum on startup ,sounds like a set of hair trimmers buzzing if you get me. serviced by a twat a few month ago who charged £150 for a bias and filter cap change.it's gona have to go to marshall i think but any ideas would help ,valves are all new (don't mean shit i know) but there not old crap ,tung sol pre's and sovtek 5881 powers,cheers

[Wildone]

Has the power source changed. Sounds like you have a open ground somewhere.

[JCM900MkIII]

Bad solder joint or replaced an old cap with new but broken one?

[mkstylee]

Thanks guys ,the buzzing seems to reduce after its been on for ten mins but still a bit concerned as it comes on with a thud as well. a good service from marshall should sort it,