Wind (Thermionic?) noise, and other strange sounds

[wicked1]

My phono (p2p aikido) started making a noise that sounds like a microphone picking up an intermittent breeze. It was one channel and I tracked it down to one of my tubes. Is that a common symptom of aging tubes?
It made another very strange sound.. The tubes are shielded. When I removed the shield on this tube it went bbbzzZZZZZzzzp. Basically, a strange buzz that increased in volume for about 2 seconds, and then decreased and stopped. I can put the shield back on, then remove it again, and every time I remove the shield it makes that 2 second long buzz.
What is that?

And last, is there any way to tell when tubes are going bad w/out a tester? I've been suspecting I'm hearing some distortion, but it's nothing major. But, I'm second guessing myself, as this hobby has ruined music for me .. I always hear distortion, and it's usually in the recording (a lot of modern music is all distorted.. entire albums sound quite bad, and a lot of old music (60's rock records) have distortion at all the loud parts) so.. maybe it's just my records.

[DF96]

Could be RF oscillation, or bad microphonics.

[Jebem]

An excessive heater to cathode voltage differential can create these problems in one or another tube, depending on the batch quality and manufacturer. Don't trust too much the datasheets. They have been written by manufactures that want their tubes to look nice.

Assuming all was well before this issue, and as You have identified the root cause on one single tube, I would just replace it and see.