I have a Carvin Vintage 16 that was always super reliable but now periodically acts up with loud noise issues, usually while warming up. I should note that it also most frequently happens when my guitar and/or pedalboard are not plugged into the input jack of the amp. It will feedback like nuts when I turn the amp on and nothing is plugged into the amp. If I then try to plug something in while the amp is starting to feedback the amp takes off like crazy with a louder much more piercing pitch. Then I'll turn it off.... unplug and re-plug in my pedalboard (which is powered during all of this everytime I've experienced this) and turn the amp switch back on and everything goes smooth for the rest of the night. Is this a situation where I might my power tubes not properly biased or one of the tubes is starting to die?? I've used this amp for at least 10 years now, I've had the tubes changed a amp technician a time or two and then me and my bandmate started to do it ourselves in the last two years, mostly just the preamp tubes tho. Thank you in advance for any advice or knowledge you might be able to throw my way. I love this amps character and tones, I do wish the spring reverb was bouncier however lol.