Why does my vinyl sound so bright?

Edle, have you ever used a wall shelf?

A wall shelf should never be mounted to a drywall panel using wall anchors. Such a mount won't hold the shelf and its load for much more time than it takes to say "Shouldn'ta done that."

A wall shelf should be mounted straight into the studs behind drywall. Those studs should not be standing on a plate that sits on the floor. The plate should transfer its load to the house foundation. In most houses that means putting the shelf on an exterior wall, not an interior partition.

If a wall shelf is not an option, a well-made floor rack has to be chosen to suit the needs of the turntable. Suspended turntables used to be said to need light racks and solid-base TT, heavy ones but floors and turntables vary. A wall shelf is really the best option.

If the only thing that changed is the wall mounted shelf, then there is a very good chance that is where the issue.

I've never wall mounted a TT, but I would think it would be harder to get the leveling, isolation, and perhaps other factors right, in general. Not to say it can't be done.

IS everything level? Any damage or changes to cartridge alignment in the process?

Arthursmuck, there's great advice here. Turntable levelling, VTA, tracking force can all contribute to bright sound.

If the VTA is "tipped up" at the back (a high arm post) the highs may be emphasized at the expense of the bass. If the turntable is out of level, the force exerted on the stylus may change angle and give an effect similar to high VTA. Also a reduction in tracking force (if the arm counterweight shifts) will press the stylus down less into the groove and that can change the tracking angle.

If your sound is brighter but also clearer, less muddy and rumbly, that's a sign you have eliminated feedback at the low end by installing your TT on the wall shelf. If this is what's happened, the feedback in the old setup may have been masking a brightness problem.