A few months ago, I inherited the use of an old series 1 Tivo that made some terrible sounds somewhat constantly. I would describe the sound as a low-pitched squeal. I blew some canned air into the fan exhaust and the volume of the sound dropped considerably, but has been building since then and further treatments have been ineffective. I finally gave in and replaced the fan and my Tivo is now as quiet as a brand new Tivo (I’m not great with similes). Moral of the story? If your Tivo makes bad noises, a $5 fan might fix it for you.
Also, don’t just google “Tivo fan.” There’s plenty of people who want to sell you a fan for $20. This one works like a champ and was $4.49 with free shipping when I bought it.
This is my opened Tivo with my new fan installed and my old fan just sitting there like a chump.