Noise at start-up of one mono-block

I have a pair of Quick-Silver mid-mono monoblocks. Over the past couple of days, each time I switch the left one on and after the tubes heat up, (about 5 to 10 minutes) the amp makes a loud buzzing sound.

If I switch the amp off and on again then the buzz stops and does not come back until the amps has been shut-off over night.

Any ideas on what the problem could?

The amps are less than a year old.
The tubes are biased and the bias holds.
The noise occurs even if the pre-amp is off.

Is this the result of a faulty input or driver tube?
The amps are less than a year old.

Contact your dealer first,if you get no satisfaction then contact the manufacturer.
Just a thought.
Switch all the tubes from one monoblock to the other.
That should tell you if it's the amp or a tube then proceed from there.
Call Quicksilver Audio and talk with Mike Sanders. He is a great guy. I am sure he will help you out.
All very logical and obvious suggestions. Thanks!
I switched the input and driver tubes on the amps. There was no noise at start-up but after about an hour listening the buzzing noise started again in the left amp.

So the input and driver tubes are ruled out as the problem. Once the amps cool, I will swap the driver tubes.
Swapped the output tubes (not the driver tubes) and the buzzing moved from the left to right side.

Conclusion, faulty or worn output tubes (EL34s).

Now, I have to replace the pair for a new matched pair. Should I replace the output tubes on both amps?
I would replace the output tubes in both amps. With fresh output tubes in both amplifiers you should get a powerful balanced sound.

Also,I recommend ordering the tubes from Quicksilver. They know best when it comes to sorting and matching tubes for their products.
Thanks Rrog for the advice.

If I am going to change all the tubes I was considering changing from EL34 to KT88.

Do you, or any one else have any experience with running the Mid-monos with KT88s.
I was going to recommend trying KT88s in your amp. I don't have experience with your amplifiers, but I have owned other Quicksilver amplifiers with KT88 tubes and the sound was very good.
I picked up a matched quad of electro-harmonix KT88's from my dealer who sold me the amps. There not from Quicksilver but I had to make a choice, no music for the long Easter week-end or wait for Quicksilver tubes. The choice was clear.

I haven't had a chance to have proper listen and the tubes probably need to burn in a bit before I come to any conclusions. Based on my first impression, the sound is much different, drums and bass are more pronounced but with less warmth.

Thanks for the input.
I am not familiar with EH KT88s. They may need a little burn-in time to sound their best.

Quicksilver has been selling Chinese KT88s for years. They sound very good. In fact I was considering Gold Lion reissues for my Dynaco MKIIIs, but all recommendations were for Shuguang Chinese KT88s.

Let us know how it goes with the EH tubes.