I have an RX 350 and I have a loud noise whenever I accelerate, it sounds like I'm driving in the wrong gear

 

Im gonna need some more information. Is it constant? Is it at certain speeds? Does it have a specific noise e.x. metal grinding, squeaking, clunking, etc.? Completely shooting in the dark Id guess based solely on the fact that you said its when you accelerate that you simply have a hole in the exhaust somewhere. If theyre small enough holes the noise wont really be prevalent until accelerating. Other things could be loose heat shield, bad wheel bearing, worn suspension components and so on.
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Also, how long have you owned the RX350? I have had one for years and it always makes a loud noise when I floor it and the motor revs up. Maybe you just have to get used to it? Finally, what year and how many miles are on it?