"A bit of noise is completley normal" ??

You are right in believing that you were fed absolute ahhhhhhhhhhhhhhhhhhhhbullshit!

There may be some preamps that have noise associated with switching sources. These are called "noisy preamps with crappy switches." Acceptable only to those who buy into the crapola that your manuf. rep. tried to feed you.

8^(

If the switch used is not a type called 'make before break' (where the connection to the new position is made before the old position is released) then it is quite normal to hear a bit of a pop or click between positions.

However- in audio applications it is a standard practice to use a 'make before break' switch in volume controls and selectors.

Other things that can affect popping or noise in the switch:

RF from your sources (digital noise can do this too)
DC coming from a tube that has internal leakage or a short.

If a tube has some slight microphonics it can also ring or react slightly when the switch is moved. If this is the case moving the switch very slowly and deliberately will prove this out.

You forgot to disclose the rest of their reply!

"Given the time and resources required to diagnose this switch which in the end was not found to be faulty or a manufacturers defect, we will accomodate you this one time only by waving our usual $500 diagnostic fee.

As a courtesy, we therefore enclose an invoice for only $300 in addition to your $2000 upgrade charge.

Please note the limited warrantee associated with your upgrade is a generous 90 days.

Please allow at least 3 months for burn in before fulling appreciating the dramatic benefits of your upgrade."

Cw, you almost had me!! But now I'd really like to know the identity of the unit in question, something I think Mr. Foster should have provided in his original post.

3 Questions:
1. If manufacturer feels that this noise is normal, why the diagnostic charge?
2. $500 diagnostic charge????? You have got to be kidding me??? Local techs in my area charge less than 1/10 of that ($30-40). Please let us know the manufacturer.
3. What was the $300 for?