Yesterday morning I hit my sidewalk(sticks up funny, my fault) with the mower and it gouged the concrete slightly. After that, I heard a noise similar to what you describe. Something just didn't sound right, like metal against metal. I shut off the PTO and waited for the blades to stop spinning, then lifted the deck. Inspection revealed that the center blade bolt (the one that hit the concrete) had come loose. I braced the deck up high with some 4X4s and tightened the bolt. Checked the other bolts as well. Noise is gone.
As far as long grass, I haven't had the chance. Now that I have the PT425, I mow about 3 times a week. It only takes me about 18 minutes to mow my one acre without doing any precise trimming. I did a good job yesterday and got real close to everything(fences, trees, etc). and it took about 30 minutes.
As far as the quality of the cut, it is very nice. I had to lower the deck 1/2 inch to get the look I want. I now have an inch down and about 2 inches up left of adjustment.
I used to mow with a late 60s simplicity with a 26" deck. It was small, but gave the best cut of any mower that I have ever seen. Nice stripe pattern on the lawn like the ball parks. The only problem was that it would not cut high enough for my taste. The PT 60" finish mower cuts much higher. It leaves a nice pattern on the lawn. It rained right after I mowed yesterday. The next time I mow, I'll take some pictures and post them.