Shops get alot of labor to do a strut job. Justfiably so... Sometimes.
It is possible the part that is in question is the
upper support mounts. Generally they get replaced if there was a specific noise issue or complaint prior to the Job being done. If this noise was not there before the Strut replacement was done , then I feel there was a problem with:
1) Installation of strut assembly was done incorrectly....loose untorqued upper/lower nut/bolts. I've seen this happen and this causes great chatter especially in the rear struts.
2)The actual Upper strut mount(s) is damaged from
disassembly or
just worn out. If it was damaged upon disassembly, I could see him asking to replace these to. Yu should have seen the part in any event. But any decent shop would ahve said YU MUST replace this! Instead of asking if yu wanted it. The story sounds funny to me too!
Be advised, 90% of the time it is the front upper strut mounts that wear out...not the rear strut mounts.
Dealers get about $100 each sometimes for these. They should be done in pairs even if one mount seems ok. They are installed while yu have the strut assembly apart.
To replace now would mean a complete tear down of the whole strut assembly again.
The shop should have been very clear and described the part and shown yu. Yu then could have made an educated decision. I can see your hesitancy of course. If the shop was straight with yu, there should have been no question on how to proceed. Yu obviously felt however yu did for a reason.
LT