An air carrier Captain reported that while on the RDU BUZZY SIX arrival; a descent clearance was not completely understood by either pilot. The frequency interference or quality was poor enough that the Controller could not hear the crew's request to verify the descent clearance when asked to do so.

Narrative

We were on the BUZZY SIX arrival to RDU at FL250. Center issued us a clearance which we did not hear clearly. we thought it sounded like a clearance to cross 20 SW of TENNI at FL240. At that time I was listening to the RDU ATIS but monitoring Center on VHF 1. I do not remember what my First Officer (the Flying Pilot) read back; but I do remember that our reception of Center was not clear; and neither the First Officer or I were certain of what the clearance had said. I came back from copying the ATIS and attempted to verify the clearance with Center; but it seemed that the Controller could not hear us; whether because of problems with the frequency we were on; or because of traffic on another frequency which he may have been working. In any case; we did not want to descend without being sure of our clearance. I again attempted to verify the clearance; and then asked Center if he had another frequency we could try. He then handed us off to the next sector; where we were cleared to cross TENNI at FL210. Suggestions to help remedy issue like this. 1. If this crossing (20 SW of TENNI at FL210) is used frequently; it might be good to put a notation on the BUZZY SIX chart. If I'd been aware of the probability of a descent clearance at that time; I probably would have put off getting the ATIS for a few minutes. 2. It seems that lots of controllers know about 'bad areas' in radio coverage in their sectors; but I don't know how organized or formalized this knowledge is. It seems that it may not be very formal; sort of 'controller lore.' I wonder if it would be possible to provide controllers with some sort of organized information about these areas; if so; controllers might avoid giving changes to crews in these areas; whenever possible.