I did some research.
Episode 509:
Osama Bin Laden Has Farty Pants
Original Air Date: 11-07-2001
Who needs Special Ops when you have Cartman's fat ass on your side? After accidentally being sent to Afghanistan, Cartman (in a tribute to WWII-era Loony Toons) and the boys take on Osama and the Taliban learning that they have a lot more in common with the Afghani children than they ever realized. Go America! Go Broncos!>> "Fleetwood Mac" is listed in the cast of characters.
Part of the transcript
General: Alright, troops, we depart for Afghanistan in five minutes! Let's move out!
Stan: [now in the base with the others] Alright, come on. We just gotta get the goat on one of these planes.
Soldier 1: [off-screen] Isn't this exciting, Tony? [the boys hide behind some boxes nearby] We're finally gonna see some action.
Tony: [the soldiers, in desert fatigues, appear] Yeah, and uh, I hear that as soon as we land we get a USO show.
Soldier 1: We do! [draws close] Stevie Nicks is goin' to perform.
Tony: Hoh, Stevie Nicks. Huh, I love her! [they move on]
Stan: [peeks out] Okay, it's clear. Come on! [moves out with the goat and the other boys. A shadow falls across them]
Soldier: [off screen] Hey you!
Tony: [aims his rifle at the boys] What the hell do you think you're doing here?!
Goat: ...Ba-a-a-a-a.
Tony: [chastened, quickly retracts the rifle] H-uh, I'm sorry, Miss Nicks, uh. [looks around] Hey guys, this is Stevie Nicks. [a black soldier walks up]
Soldier 2: Oh wow!
Goat: ...Ma-a-a-a-a.
Soldier 3: Uh, can I get a picture
Soldier 4: Miss Nicks. Over here, Miss Nicks! [takes a picture]
Goat: ...Ma-a-a-a-a.
Tony: Oh... M- Miss Nicks, I... I don't wanna bother you, but... could you sing a quick Fleetwood Mac for us. Could ya?
Other Soldiers: Oh yeah. Please. Come on, come on. Please. Yeah.
Goat: ...Ma-a-a-a-a. Ma-a-a-a-a.
Soldiers: Oh! No way! That was wild! That was great!
Soldier 3: Wait till I tell my sister about this; she is gonna flip!
Stan: Well, uh, we've gotta get Miss Nicks on the plane to Afghanistan, guys.
Tony: Oh, can we just get a-
Stan: [turns right and walks off] Ah, sorry. Mss Nicks isn't answering any more questions.
Tony: Oh, sure, we understand. Move along. [the soldiers watch the goat walk away with the boys]
Soldier 3: ...She looks great