Audio Research Ref 5 SE ting noise

Recently bought a used ARC Ref 5 SE from a dealer. I am in love with the sound! I noticed that when i switch inputs - there is a momentary "TING" noise that comes out of the speakers. It's almost like a very sharp bell sound. I hear it in both channels. It doesnt vary with the volume level. The tubes have about 1600hrs on them. 6H30Ps are Electro harmonic and the 6550 is a JJ Black Sable. I am connecting with balanced connections. Turning the upstream DAC on/off doesnt seem to make a difference. I might call ARC sometime - but wanted to check if others have seen this issue.

Upscale audio FAQ section mentions something about this - not on 6H30Ps - but other types. 

https://www.upscaleaudio.com/pages/tube-basics-and-frequently-asked-questions 

The 6DJ8/6922/7308 family of tubes is a special lot and are prone to be sensitive to vibration. That does not mean all of them are microphonic by definition; though some are. What's this mean for you? In high gain pre-amps, you may hear a slight "TING!" when flipping some switches. Usually this is caused by the grid wires picking up vibration through the tube pins. We listen to each tube in circuit and ship tubes according to the product it goes into, in order to give you the best results. If you own a preamp from Audible Illusions or CAT (to name a couple), and you experience a slight ring for a second when you bang on the pre-amp or flip switches, don't sweat it... unless you plan on playing bongos on your pre-amp while the music playing. I must say... if that's your plan... you may want to re-think your strategy.