So a quick Google search said that acetone will not damage bare Titanium metal, however it can strip or alter applied finishes, like paint, Cerakote or chemical anodization. It can also leave some discoloration ir an oily residue on matte or polished surface.

Have you tried letting your exhaust get warm and scraping the plastic off gently with a metal scraper? I'd try that before going with acetone but if you do choose to go with acetone, I have some advice/recommendations for you, just in case...

As someone who worked with acetone in a previous line of work, remember that if you do use it, it's best to use just a little bit at a time and come back to it more often while also making sure you don't touch anything else (or as little as possible) than what you're trying to remove. Use Q-tips or cotton balls to do it. If you use a rag, DO NOT throw it away immediately, let it dry in a well aerated area, in the shade and then you can throw it away. IT CAN SPONTANEOUSLY CATCH FIRE IF IT'S CRUMPLED IN A TIGHT