Put a lid on it (or not?)

not necessary to tap on tubes it’s enough to tap on amp/preamp chassis to hear tube microphony. also if you softly touch with palm of your finger you may hear either hum or noise.

My LP12 has a dust cover. I like it. Keeps platter and Tonearm cleaner than Kuzma Stabi even w/ a cloth cover on it. But I am a proponent of the long ICs / short speaker cables school. Only amps and speakers in the listening room! At low volume no problem with eguipment and TT in room; but at normal to Rock Out volumes IT IS a problem!! Even wth all the racks, spikes, footers, isolation platforms, that I have tried in last 28yrs out of 45yrs; I prefer the long IC/ short speaker cable and TTs and other eguipment OUT of the room! 
Sure it is a compromise; but so is the short ICs and all equipment stacked between the speakers school. 
Yes, I am one of the lucky guys. Dedicated Room, no kids, no pets, great WAF. 
I bought better ICs than tons of $ on racks, platforms, spikes, you name it !!! It is easier to clean, change out a piece of eguipment for audition, more pleasing to the eyes, and sounds better to these ears. 
Listen, Trust your Ears,
Best to all on this Journey!

I've been doing this with my Rogue Ares phono preamp. The lid+sides is one piece of sheet metal of relatively low gauge; any disturbance and it rings like a bell -- not a good thing for a tube phono stage. Plus the weird tube cage thingy is ugly. So, off with the lid.

Meanwhile my Rogue Hera preamp chassis is machined aluminum, and works quite well to isolate the components/tubes inside, so the thick/heavy lid stays on.

And as has been said before -- DON'T tap your running, hot tubes with a fingernail, etc. Tap around them, or at most use a light touch with the soft part of finger (depending on how hot).

Yes, I am one of the lucky guys. Dedicated Room, no kids, no pets, great WAF.

Is it definition of audiophile luck? 
Is it no pets/kids or no wife with plenty of hi-end stuff?

I'm happy with my parrot, but had my luck much better when my kids lived with me though.

As just another audio nut with his own opinion and the related anatomy to go with it, here's my take...

Covers on a normal turntable playing vinyl causes an unacceptable sound quality. And sure, if you have the money for a big isolation platform and your cover fits over the entirety of the whole TT, then I can see where it would be workable. 

As to amps, I had a fabricator make a Faraday cage just for the amp transformers, leaving the tubes open to the room. It greatly improved the sound, but the main power transformer, while working within its operating temperature range, got hot enough to degrade the sound after about an hour. So, then i installed a cooling fan within the cage. Problem solved.

After buying custom racks, all kinds of footers, including custom made pointy footers from solid brass, I went to mass loading. At the one large aluminum recycling place in north Denver, they have every size of solid blocks of this metal, including 2 by 4's.  Placing these and moving them around to find the right spot on small & large components was beneficial and inexpensive.

A word about vinyl. I somewhat scientifically cleaned 1,000+ records with a Loricraft followed by critical listening. The most important things learned were that regardless of all the other variables, you MUST not use rubbing alcohol as it is to strong of a solvent (use denatured up to a maximum of 25% in solution) and you MUST re-lubricate every record post cleaning, even if the cleaning chemicals suggest they do so. The only product I found suitable was a tiny amount of Gruv-Glide applied per the directions. Otherwise the diamond will cut the crap out of a dry, clean record and ultimately degrade the sound. I estimated that 16 tiny pops were added each time a "dry" record was played. Lastly, always clean every record before play, new or used. New records are greasy and sound smeared and dull. Used records flip dirt into the cartridge wrecking the cart suspension.

Bill Utz