I am looking at either installing:
FM modulator: https://www.crutchfield.com/p_142FMM...RoCp6AQAvD_BwE
-or-
Retro Manufactoring Grand Prix: https://www.retromanufacturing.com/p...41507949609116

I don't mind spending the extra money ($219 vs $56) if there will be a drastic difference in quality. Cigarette lighter bluetooth receiver/fm transmitter works great up until the radio is at 90% or so. After that there is audible static. I've cleaned the braided firewall ground already but I could try a new one to see if it makes a difference. Also wired up a new cigarette lighter on a different circuit but the static is still there, unfortunately.

 

Nevermind. I soldered a line in to the cassette circuit.