Tube whistling

Hi, I have a Counterpoint SA7 preamp (the early model) not the 7.1.
It uses (2) 12au7 tubes in the line stage and (2) 12ax7 in the phono.
If you are familiar with this unit, then you know about its problem with microphony.
That is something that can be reasonably tamed but another problem the unit has is a tendency for the line stage (12au7) tubes to ‘whistle’. That is, a high pitched sound introduced into the signal that changes pitch and tends not to go away until you actually tap the tube that is causing it. It comes and goes, is at a very high pitch and not loud but definitely can ruin the listening experience. I was told that there is a modification that can be performed to allow the unit to run 6DJ8 tubes in the line stage that will alleviate this problem. My first question is does anyone know how to tame this problem without such a modification? Let me point out also that I have tried tube dampeners, isolating the unit with special feet and how loud or quiet I play the stereo has no affect on the outcome. My second question is has anyone performed the modification that allows the use of 6DJ8 tubes within this unit? I do not wish to purchase new tubes just to see if that will cure the problem for a short while unless of course that is actually something that someone of knowledge is going to tell me…
In my own experience with tubed amps and pre-amps, typical line stage tubes usually last about 6 months to 2 years depending on the application. True West German Telefunkens will usually last twice as long as other brands. It sounds to me that you should probably splurge for a new set of tubes, and, if microphony is your main concern, you will be better off ordering them for "moving coil phono stage" usage.
thank you for the response...i have a set of telefunkens in another unit and they have lasted many years but they are not 12au7s...could anyone tell me, is whistling a sign of a worn out tube? I have never experienced this in any other unit or with any other tubes...
Get new tubes,they sound shot.
thanks again...but if you read my post carefully you will see that microphony is not my main whistling is my main concern...i have found through the years that worn out tubes either cause grungy noise or just lifeless sound...not whistling. Thank you for the response but I am hoping for an answer from someone who knows of this problem with this unit, not just generic suggestions. Once again, can whistling be a sign of worn out tubes? I must admit though two out of two replies suggesting new tubes seems a direction that might be taken.
This is from the Alta Vista webpage...{The unit has two 12AX7 tubes in the phono stage and originally had two 12Au7's in the line stage. Later versions used two 6DJ8's in the line stage to overcome a tendency of the older tube to "whistle."}
Anytime ( speaking from experience ) you get any noise from a tube,,If you can find the tube making the noise..Get rid of it..If you don't you could pay a higher price shortly down the road.....
i've had similar problems with 12ax7s in an arc sp16. shuffling tube positions has eliminated it on several occasions. the tubes are just under 2 years old. I first heard the problem about a year ago. the consensus opinion is that the noise results from one or more lesser performing tubes. The solution is to replace any tubes causing noise. I'll likely be replacing all 6 12ax7s in the arc sometime soon if/when the problem recurs.
I have a SA-7 but with 6DJ8's in the line section.
Call Mike E. at Alta Visa Audio and he may have suggestions for you. Better yet send it to him and have it upgraged you will not regret it. I did the line stage, volume control, part of the phono upgrade, and had the RCA jacks changed. The change in sound is well worth the cost.