Mine did that, both the original and the warranty replacement, when water
got down in there (original/maldesigned pollen filter kit induced water to
enter...).
The way it sounded and varied with blower speed said to me that the blower
motor bearings must've been affected, but I never ascertained this. Out of
empathy for those bearings, though, I bumped up the fan speed up a bit (I
never use the Auto fan speed mode) to keep the squeal/vibration at bay.
The flashing lights seem to indicate, among other possibilities, that the
blower motor efficiency is substandard. Even if there was no water inside
the car, a soaked pollen filter's added restriction should still be enough
to make the motor work too hard...
The last time there was significant water intrusion was about a year ago.
The filter got saturated. The lights flashed every time I started the car
for weeks. They'd stop flashing after a while (minutes). Everything
worked OK. I no longer had to bump the blower motor speed to avoid
squealing. But just moving the key from position II to position I would
re-initiate the blinking ECC LEDs. Within about a month or so the LED
flashing routine disappeared.
I checked for codes once (I'm not sure the dealer ever did), this year; I
found one (something about a controller) that never would clear.
Meanwhile, water's not made it into the passenger footwell area (via the
HVAC intake ducting) since I've changed (forced to, by Volvo) to the newer
pollen filters (but I don't get many tests in my climate). I think they
flashed once since that last extended bout, without any squealing, but
among the current filters the only one that's worth a damn is a
hybrid/charcoal sandwich that IS more restrictive -- so I know the motor's
working harder than it was meant to, so I ignore it (there are no symptoms;
everything [still] works).
So I'd only worry about it if there's a real problem that sticks around.
I sometimes think this is the kind of stuff that passes for personality in
these cars.
- Dave; '95 854T, 101K mi

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