Problems with peavey 5150 II distortion channel

[georgioslukai]

I bought a 5150 II head about 7 months ago with all-new tubes in it. Recently, it started emitting a soft hissing sound that comes and goes about every 10 seconds, but only on the distortion channel. It makes this hissing noise regardless of the pre or post gain levels. It also makes the noise initially after i turn the amp on after having it on standby for a minute. I haven't messed around with the tubes or anything like that since it started making these noises. I really don't know much about it so any advice on this issue would be greatly appreciated. Thanks in advance.

[Jazz P Bass]

Well, you have narrowed down the problem, slightly.
If the pre, post controls do not effect the noise, then the problem is after those controls.
Honestly, it could be a number of things.
Bad soldering, a faulty component....
Time to troubleshoot.