my tubes are hissing non - stop

just upgraded from a STEREO bat vk55 to a pair of bat vk55 mono blocks whereby am pairing with a bat vk32 pre amp.

initial 7 days of listening was almost hiss / noise free until recently where the hissing sound was audibily louder and as i turn the volume higher, i began to hear popping sound.

a few observations

1. the hissing sound remains same level regardless volume is high or low.

2. hissing sound comes on only after pre amp is turned on. if only power amp is on, no hissing sound...

3. tapping (even slightly harder) on power amps/tubes in the power amps did not bring about any change on the hissig sound. does this mean that the power amps is not teh culprit?

4. dun think its the quality of the current as the set up for the transformer/multiplugs did not change at all.

5. i have not inspected the tubes in the pre amps shld i and how?

this is suppose to be an upgrade but ....

am at a this a current issue or a tube issue and is it an issue in the pre/power ... looks v tricky to troubleshoot
Try replacing the tubes in the pre. Sounds like the place to start.
Generally - can't the a faulty tube in the power amps make such a hissing sound even before pre-amp is turned on?
This is a very common occurrence when tubes are on their way out. Sounds to me like your preamp tubes need to be replaced. Until the preamp is turned and there is a line level or phono signal, the power amp should be quiet. Since you just upgraded, you should contact the technician that serviced it and inform him of this situation anyway.
Sorry, should have read that it was the power amp that was upgraded. In most cases replacing tubes is just a matter of removing the preamp cover and removing the tubes from their sockets and replacing them the same way. Just check that the pins are lined up properly with the tube socket when you instsll the new tubes. You shouldn't have a problem with it. When you remove the cover, you will be better able to determine whether it will be a simple task, if not, put the cover back on and have someone do it for you. One other thing, Just make sure the preamp is turned off when you do this. :>)
If your cd player can be directly connected to the amps I would try that to see if the problem is still there,if gone then the pre amp would be suspect;did you rotate a new pair of innerconnects to see if that is the problem;mostly not in my opinion but it would remove the cables as a suspect.
for the records ...

the power lies in the pre amp: vk32

where 1 of the tubes 6922 was flashing like a light bulb / internal lightning when technician changed it.

swapped a new preamp and now all is clear .... but 1st time witnessing a 6922 tube flashing light a lightbulb turning on...

tks all for kind advice