98 Tacoma power steering problems

Hey guys, new to the forum so I don't know if anything like this is already addressed on the site. I drive a 98 Tacoma 4cyl 2.7L with 270,000 miles. Running pretty strong. But my power steering is giving me a little bit of trouble. It hums right from start up and the hum turns to a growl when cranking the wheel although when its locked all the way left or right the noise completely stops. And the hum intensity and pitch is pretty much parallel to acceleration. So the harder I rev the engine, like getting up to speed on the freeway, the more intense the hum is. I just flushed the old fluid yesterday till it was the same color coming out as it was going in and refilled the reservoir a few times till it was at the cold line even after locking the steering wheel left & right. I'm going to hit the reservoir filter screen with some break clean tonight to see if that helps but I think the pump is just dying. Any advice/solutions/ideas welcome. Thanks guys

 

I know they make an additive that's should help quiet the pump, but I never had to use it. Do a search for you problem on this site you should find some info. With that many miles, it really could be time for a new pump.