Dunlop SP Sport 275-35-R18 RF howling

[jpg2003]

Rear tires on 535 are howling. Dropped the the tire pressure down to about 36 and it got worse. Tires have about 20,000 or so miles. Bought wheels and tires used, so not sure what pressures were in them. What causes this. Can I minimize the noise or do I have to replace with tires.....Thanks.

[Gary@Tirerack]

Performance summer tires like this will get progressively louder as they wear, and most only last about 20,000-25,000 miles on average. These are likely near the end of their useful life.

Tires http://www.tirerack.com/a.jsp?a=AB2&url=/tires/index.jsp