Bedrock tube guitar amp farting

Please no jokes.

I have a 100 watt bedrock tube guitar amp that i already replaced all tubes in. After being on about 5 min it starts making this terrible farting sound. i must turn it off immediatly or it blows the fuse. Any ideas where i can look myself before taking it to a shop??
thanks
dnelsonrocks@yahoo.com

Can you post a schematic for it?.

A tweaked version of the Marshall designs using an EL34 output stage?

Tube amp farting is usually an oscillation caused by voltage breakdown of a part, usually a cap. If you don't have much test equipment try replacing the electros (yep it will cost a bit) and also the cap breaking down could by a polyester type.