451S speed changing and buffer underrun problem

i’ve had my 451S for several month now, and its been working good for me, i even did use 451S@851S but i reverted back to GSB7 because to me, there was no point for 8x +r burning

well now i have a weird problem with alcohol, sometimes the speed drops while burning, and other times the program just lags my entire windows, and thus creating buffer underrun…

i used to do this all the time, surfing the net and etc while burning discs, and there was no noticable lag and the discs came out perfect…

i wonder what happened, any help is apperciated.

Is your drive in DMA mode? Is there anything running in the background? Could you use Nero CD-DVD Speed to check the drive’s burst rate?