Noise during Acceleration. Starts at 5200 RPMs, 150,000 miles

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For the past two years this Lexus has a hard to describe loud noise, like a high speed scraping, well you reach 5200 RPMs. To reproduce the noise, all you do from a stop is floor it and when it reaches 5200 the noise happens. Then the trans shifts and the RPMs drop to 4600 and the noise is still there, but slightly less. It isn't speed dependent and A/C or alternator load doesn't matter. I just changed the timing and standard belts and pulleys. I was going to try it with the A/C and Alternator belt removed. Then if I can drive it with the P/S belt removed. I replaced the exhaust front pipe and welded all holes in the exhaust behind the rear cat. In the two years the noise hasn't gotten any worse or less.