I bought the LDW851s about 2 months ago and almost sent it back in the first week I had it. I bought some Bulkpaq -R media from Novatech in Portsmouth for about Â£13 for 25 on a spindle. Each time I burned a disk there was this kind of crunching noise and my standalone had no end of problems reading them.
I flashed to the latest firmware, GSOF?? I think, which made it even worse. Then I discovered the k-probe tool and scanned some of the discs I'd written. I had PI errors up in the 300s and when It first started scanning it gave me an error, something like 'servo error, media error - servo tracking media'.
I was convinced my drive was bad and was all ready to send it back. Then I found some Ritek 4x -R media on SVP (www.svp.co.uk) for about Â£13 for 25 and thought I'd give them a whirl before I sent the drive back.
My first spindle of 25 came and went without a single coaster. PI errors average 2-3 and PO 0.005. Superb burning with these discs and I'm getting better results on GSOC, though I hear that GSOF may be better for +R.
My advice is test some discs you've written with k-probe and see what the errors are like. Also, buy some quality media before you start flashing the drive. Maybe someone else here will give you different advice but I rekon bad results are probably due to bad media 99% of the time.