You probably burned those discs with multi-session turned on. Typically you used Nero and burned a data disc. When you clicked the option to burn, you were presented with some screen about multi-session and you selected "yes".
When you burn a disc with multi-session enabled, any drive trying to read the disc first attempts to find the last session on the disc, even if you only have one session burned. With some drives, this takes some time and produces some awful noises like the disc got stuck in the drive and the motor is trying to dislodge it or something. This is normal and does not damage the disc or drive in any way. I have a Pioneer DVD-ROM drive that does exactly that.
If you don't really intend to add any more data to a disc, there is no reason to use multi-session. A disc burned without multi-session will probably read up faster on your drive because it doesn't have to find the last session. The drive also won't make those awful noises. If you don't believe me, try it and see.