Sounds like the color wheel or possibly one of the internal cooling fans. ShopJimmy lists that for $80 but is out-of-stock. Expect to replace the DMD as well when you start seeing white/black dots. That lists for $75. Looks like the fans are $20. If you can assemble a computer from parts, you can do pretty-much all of the maintenance on these DLP sets.
I have a Mitsubishi DLP and plan to keep it running until I can pick up a 4K TV on the cheap.
I'd hold off on buying ANY new TV until HDMI 2.0 and/or DisplayPort >1.2 becames standard on TV sets.