Have you ever downloaded music and found it strained at high pitches giving a weird vibration effect?
The fact you haven’t noticed that effect playing it on the computer makes me think that most probably something in the burning process has gone wrong. Yet to be perfectly sure did you listen the files, downloaded on your hard disc and the CD you have burnt later on the same loudspeaker system? If there is no difference in the quality, then the downloaded files are partially corrupted and I am afraid almost nothing can be done, but to try to download from another site (the reason could hardly be in the network traffic). The difference in the quality on the other hand would mean a data corruption in the CD burning. There is nothing wrong to use recordable CDs (all music and data I have downloaded is on recordable CDs, I don’t use rewritable CDs at all, USB flash devices are much more comfortable for that and many people believe they will soon replace CDs and DVDs, follow the link in Sources below for some comparison), they are very cheap (several cents per disc) and you simply throw away
