[IRCA] PL-606 audio pumping on 75dBu signal? :( (also volume observations)

[Stephen Airy <pianoplayer88key@xxxxxxxxx>]

Hi all... I've noticed that even on some strong signals my PL-606 is exhibiting audio pumping.  I recorded a few minutes of 1090 XEPRS in the early/mid afternoon a couple days ago, capturing a couple commercials and a few batters in a Padres vs Braves baseball game:
http://tinyurl.com/PL606-1090-XEPRS-pumping-75dBu
The RSSI was 75 dBu (occasionally hit 76 dBu), and S/N (on the display) ranged from 2 dB to 25 dB (and was generally 25 dB when the modulation was relatively quiet, like when it was only crowd noise being heard).  The PL-606 was inductively coupled to a Select-A-Tenna (on the side to notch down a 75dBu signal on 1130 and an 81dBu signal (both barefoot readings) on 1170) and a chain-link fence.  (RSSI on the stock antenna is somewhere around 52-54 dBu or so, IIRC.)  Audio bandwidth was set at 4 kHz (it says 6 kHz, but it's actually 4 kHz).
Anyone have any idea why the PL-606 would be having audio pumping on such a strong signal?
 
 
I also used two PLL radios (Panasonic RQ-SW20 tuned to 530 and Panasonic RQ-SW44V tuned to 531) to generate a 1 kHz tone on 980 kHz (completely burying a weak signal from KFWB Los Angeles, btw), and recorded my PL-606's volume levels from 0 to 30.  After turning it on I increased the volume 1 notch per second, approximately.  (I didn't time it with a clock, though.)
http://tinyurl.com/PL606-VolRange-24bitWav - that's an uncompressed 24-bit 22.05 kHz mono wave file, if you want to download it & analyze it yourself.  RSSI on the PL-606 with the two Panasonics generating the test signal was 70 dBu, S/N was 0 dB.
If you don't want to download, here are the volume levels, as reported in Audacity 1.3, relative to full scale (0dB):
00  -65.1 dB
01  -65.5 dB        11  -18.0 dB        21   -4.2 dB
02  -64.9 dB        12  -15.9 dB        22   -4.1 dB
03  -58.3 dB        13  -16.1 dB        23   -4.0 dB
04  -60.1 dB        14  -14.3 dB        24   -3.9 dB
05  -55.8 dB        15  -10.9 dB        25   -3.7 dB
06  -36.8 dB        16   -9.1 dB        26   -2.7 dB
07  -32.0 dB        17   -7.5 dB        27   -1.8 dB
08  -28.3 dB        18   -6.4 dB        28   -0.9 dB
09  -23.1 dB        19   -5.2 dB        29   -0.8 dB
10  -21.0 dB        20   -4.5 dB        30   -0.8 dB
I noticed that when going up from 3 to 4 the level actually decreases, and when going up from 5 to 6 there's almost a 20dB increase!
 
(I'd post this to the ultralightdx yahoo group, but I don't currently have posting priveleges there. :( )
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