Well, the muffler problem turned lifter problem has been solved.

To briefly recap, when my normally quiet engine all of the sudden turned
loud, I immediately suspected the muffler. What I was not hearing was
the loud tapping of a stuck hydraulic lifter -- my mechanic pointed this
out to me. He suggested an oil change with some Slick 50.

I did the oil change but passed on the Slick 50. I have heard
questionable things about them before and several people on the list
wrote me to warn me about this stuff. Taking the advice of Sean and
Justin, I changed the oil and added 10W40 which is a little lighter and
therefore would help to flush out my lifter. Sure enough, after starting
the car with the new oil in, my noise went away as the oil light turned
off. What a relief. I think the force of the new oil flowing through the
engine was enough to flush away the offending particle(s). What also
helped was letting the oil drain for an hour or so (try that at Jiffy
Lube).

Anyway, thanks again to all those who responded. With this list, I feel
like I have a protective extended family ;-)

Scott Semyan
'85 Westie
Seattle