2000 Tundra 4.7 engine roar at 2k to 3k rpm

Just noticed this today after I changed my oil the previous day. Anytime I accelerate and go over 2k rpm, there's this loud roar. Check engine light also has turned on. Anyone know what this could be?

 

Also anytime I start it, it shoots to almost 2k rpm with the same roar and then goes down to 800 rpm

 

The roar is normally associated with the radiator fan. You'll need to get the code read to see what set the CEL. I can't speculate if they're related though.

 

Missing your catalytic converters?

A code reader will help tell you what's causing that check engine light and where to start.

 

Oh, damn. That hadn't even occurred to me. Excellent potential diagnosis!

 

Any time your check engine light is on, before you post on the internet looking for help, please go to your local auto parts store and have them scan codes, it's a service nearly all major chains provide for free.

We can sit here and guess all day long what the problem is with weird, vague, and/or ambiguous symptoms. But chances are the code that's set at the time the cash-money light goes off will indicate the issue.

Do us all a favor, go get scanned, and let us know what the code is. I'm guessing it's going to point to an O2 sensor. But that's the best I can give you w/o codes, a wild ass guess.