If you're worried I recommend changing the transmission oil.. I did this when I bought my car. It's easy to do but you have to use Volvo's synthetic blend (dealer item). It's good preventative maintenance and will be one less worry as well.
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'94 855 5spd 'Drew' 203,000 Miles -Currently laid up getting a good internal cleaning and tomorrow a nice used head, new wires, seals and stuff-

I have a bit of gear noise in my manual transmission, too.

If you have the transmission split I would replace the clutch and
throw-out bearing. It is a good 8 hours labor to do that later
and I bet the parts are not too expensive so much cheaper to do
it now.

By the way, my throw-out bearing sometimes squeels like a pig when the
clutch is let out. This started at about 35K miles and it seems that
the throw-out bearings sometimes do this. It still works but I suspect
I'll have to replace it before the clutch is worn out.

I get the same sound on my 1995 850 Manual on occassion. Hasn't really bothered me, and it has been there for about 60K and no problems. Shifts smooth etc. I have just learned to live with the little quarks of the car. Overall has been excellent and I am a big fan of the cars.

1995 850 Wagon 116,000 5 Speed
1999 S70 Sedan 80,000 5 Speed


J-

Let me know if you find anything serious that is going on.

I noticed the same thing on mine. I just assumed it was normal gear noise. If you find that it's something different please post it.
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'94 855 5spd 'Drew' 203,000 Miles -Currently laid up getting a good internal cleaning and tomorrow a nice used head, new wires, seals and stuff-