Really need advice and opinions?

So I recently bought my first amplifier a Traynor YCV50. Great sounding amp IMHO. I basically have a few questions for you guys regarding this amp.
Around the 2nd day of using it lightly at the house I noticed some tube rattle when I would play a low G or F# note on the guitar, but it wasn't too bad. Last night I went and played with a loud drummer and had the amp really cranked, today I've noticed back at home that the tube rattle is a bit worse and more audible(sounds like it might be getting amplified through the speaker? ). This tube rattle I'm hearing is usually one of the preamp tubes right ? Apparently mine has Sovtek preamp tubes in it. I should be able to find the right tube by gently tapping it with a pencil correct ?

At the end of the night the drummer wanted to try out my guitar and new amp so I let him. When he was done he reached back and turned the amp off before I could tell him to first put it on standby; the amp made a slight popping noise when he turned it off(didn't sound unusual though, just the generic kind of channel switching type pop). Could this have harmed my amplifier ?

I also noticed that when I had the amp on standby today before I played it was making some audible hum through the speaker that kind of cut in and out a bit. It did this for about 10-15 seconds, and also did the same thing when I put it in standby when I was done playing around 30 minutes later. What could be causing this ? I'm a little concerned that my new amp may already be developing some problems. Any and all advice is greatly appreciated. Thanks guys!

 

So heres a bit of an update on the standby noise issue. What I'm getting is a bit of crackle and some slight hum when the amp is in standby mode.
Any thoughts on what this could be?

 

seems strange on a new amp that has maybe 8 hours of use though.

 

Another update. I tried the amp in standby for about 5 minutes today with no hum or crackling noises. Proceeded to play the amp for about 20 minutes.
The tube rattle has definitely gotten worse, and it is for sure coming through the speaker as noise(not sure what microphonics sound like though, but noise none the less!).
After playing for about 20 minutes with no crackling or anything, I put the amp back in standby and the crackle started. It would crackle intermittently with some hum in between and eventually stopped crackling but the hum remained constant until I turned the amp off.
I looked at the power tubes while it was still on standby and it kind of looked like one of them was glowing a bit brighter than the other.
Some advice would be greatly appreciated!

 

So the hum and crackle when on standby aren't likely caused by a bad tube ? A more serious issue than a bad tube ?
Well I have a retube kit and a bias probe and multi-meter, so I think I'll do that. I just need to know one thing though, what setting should I put the multi-meter on and what should I bias KT77 to ?

 

So I replaced all the stock Sovtek 12ax7 tubes with new 12ax7 tubes. I put a Tungsol in V1, Mullard reissue in V2, and a JJ in V3(phase inverter).
After that I plugged my guitar back in and turned the amp to standby mode. I still had the intermittent crackle with hum, did some testing and found that the hum could be completely silenced by the master volume knob or made louder by turning the master volume up higher(interesting!).
I then turned the amp on and started to play, right off the bat I noticed an improvement in the tone and feel of the amp. The gain channel had a bit more juice/grit to it, I was very happy with this.
The tube rattle was still there however. Now I tried gently tapping the power tubes with the eraser end of a pencil. The first tube did nothing, the second tube(the one that seemed to be glowing a little brighter in standby mode) made some noise when I tapped it. I also tried tapping that tube in standby mode and got the same crackling and hum when it was tapped; so I'm pretty sure this is the problem tube.
So can someone tell me what setting to put my multi-meter on for biasing? And what milliamps should I set a KT77 to?