Dan,
was on sabbatical over the holiday, and just happened to check the non-specific, rather than older vehicles.
the rattle, as you step on the brake goes away? and you say "p" or "n" so I guess it's an auto?
well, it could be a VSS (vehicle speed sensor), since it gets its feedback from the wheel/ABS sensors, and the minor tap/vibration smooths out as the brake pedal is applied. VSS @ Audi is about $30-40.USD, and is located on the driver's side of the trans, forward of the tailshaft (if it's AWD)
BUT--- I think you should drive the vehicle up on ramps, and then even jack up and jack stand the rear, and get underneath.
the 90 series had AMPLE heat shields, and one of them could have rusted or come loose, and braking eases the rattle because the engine idles differently, due to vacuum, and the tailpipe doesn't smack the shields. if excess mileage, and/or it is rusted, or broken, I'd just remove completely. the shield that is behind the trans is the most likely culprit, as it wraps the tail of the trans, and goes up into the well around where the "Y" pipe converges to one pipe. you'll get better gas mileage if you rip this one out and pitch it, as it has probably collected in its vast cavity above it an additional 40lbs of dried mud and road debri.
as to the brake lights, if not the fuse, could be a stop light switch going bad, and blowing the fuse, or if you live in a humid climate, water/moisture in the back light lenses.
hope this helps,
chris
nrt racing
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