Am I overpowering my drivers when they

Budding enthusiast here trying to figure out why the drivers in my speakers "pop" at medium-high volumes. I've recently decided to explore the world of "new vintage" speakers and amps (70's and 80's era stuff) in 2 channel for listening to music after a few years of 5 channel supported by a Harmon Kardon AVR 320, Axiom M3Ti mains, Axiom 150 center, Wharfdale surrounds, and an Acoustic Research 12" Sub. This setup just didn't have the presence and power for music that I felt I could get with bigger drivers/enclosures. The little Axiom's are impressive speakers with wonderful detail and clarity, but their small drivers/enclosure limit their capabilities. So I hit Craig's list and started my quest to put together an inexpensive yet repectable system using proven and repectable older gear. First I acquired a Carver 1090 integrated amp to power my 2 channel system and have been picking up speakers as I find something interesting and inexpensive. So far the collection includes Pardigm 5SE's, Polk Monitor 10A's, and Cerwin Vega VS120's. I'm also using an Onkyo 7-band EQ and usually have the loudness activated on the Carver. Problem is, at volumes that are just starting to approach "loud" (output on the Carver showing about 40-60 watts and volume knob at about 30%)...and by "loud" I mean you could still carry on a conversation without yelling, but you'd have to speak loudly...the drivers on the Polks (two 6.5" drivers/speaker and a 10" PR) and the Paradigms (one 8" driver/speaker) start to "pop", like they are being pushed too hard. Maybe my expectations are set a little too high, but I thought either of these speakers, with a clean amp like the Carver (it is a clean amp, right?), could get pushed pretty hard before the drivers started to make that "pop" noise that I always associated with a driver that is being driven too hard. The bass level knob is dead in the middle (would that be "flat"?) on the Carver and the two lowest frequencies on the EQ are just a little above the half-way mark (zero). The Carver has a little needle that shows db output, and I think I'm seeing about -20 or so when the drivers start to pop. Both speakers have rubber surrounds on the drivers and they all look good. At medium volumes I'm very impressed with both the Polks and the Paradigms, but I was hoping I could get a little more out of 'em before they started to lose composure. Could there be something wrong with the amp?