CD/DVD drives will speed up and slow down randomly

I have a Dell Inspiron 531 Desktop a little over a year old. The CD/DVD drives will randomly spin very fast for several minutes and then slow down and then will randomly do it again. This will happen even if there is not a disc in either drive. It makes enough noise to be very distracting.

Processor, Athlon 64X2 For Desktops, 5000+, 2.6, 1MB, 2C 65W, G2

Hard Drive, 320G, S2, 7.2K, 16M Lead Free, Samsung

Assembly, Compact Disk Read Write/Digital Video Disk Drive48X, Half Height, BARE, PBDS

Assembly, DVD+/-RW..., 16X, Bare Hitachi LG Data Storage

Assembly, Cable, Serial Ata Optical, Matrix, smith, mini Tower

DVD/CD-ROM Drives

HL-DT-ST DVD+RW GSA-HT3N SCSI CD Rom device

PBDS CDRWDVD DH-48C2S SCSI CD Rom device

Thank you for any help,

Garry