Thank you all
Thank you PHOOZLES and SUGARCATMOM for this enlightening discussion back in 2007!
This thread began almost identical to what is currently going on in our home. Healthy over weight older cat Yoshi (8 years) introduced to Denver a younger 10 month old kitten brought into home (a rescue from Humane Society).
After several weeks, Yoshi develops a rough purr and a nasty hairball-like cough, which only occurs while purring. Initially didn't think much of it, after all, the two were getting along, grooming each other, playing, just chalked it up to extra fur being ingested, and encouraged Yoshi to ex-spell the furrballs, which never came out. This has been going on for just under 2 weeks, and we are growing concerned.
Thank you again for posting this info for all to see. I don't know if this solves our situation, but at least it provides additional knowledge when we visit the vet next week.