My passenger door speaker blew a few days ago ( I was playing "No Bulbs" by The Fall if you care to know). It's very annoying. I could probably get a speaker that would fit it, but I have no idea how to remove that cover..there don't appear to be any screws or clamps. Has anyone here ever done this?

I just ordered a pair of front door speakers from Crutchfield. They recomended a 4" with plate to make them fit. The OE speakers were 5.250 X 2.125. I think the thickness of the speaker might be so close that some brands won't fit.You will need a torks bit to remove the old speaker {a small set of Torks bits should cost about $6.00}
I'll keep you posted as how the speakers work out.
Does anyone have any ideas on what to use as replacements for the tweeters in the dash on my 97 850 wagon.

they just snap on and off.

Correct...take s screw driver and put tape around it so you won't scratch the cover when you pry the mesh off. Once this is off, you'll see the 3, or was it 4 screws that come out to take the speaker out. The wiring is a quick connect plastic piece...very easy. Now, the question is where to get another speaker. I would first try a yard, like http://www.erievovo.com/ If you still can't find one then the dealer it is...what I had to do when I had one go bad...a few years ago, they were about $35 or $40 each. I wouldn't try to put a different speaker in there unless you're changing the other one too and the Ohms match.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.