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Paul,
If it comes from the front, check the nut at the top of the strut tube that holds the shock insert in place. If it's loose it will knock when you drive, but you won't notice it just by bouncing the car. The gas charge (if there is any left) will take up the slack faster than you can bounce it.
Jack the car up by the chassis to extend the strut and get the bumper/dust boot out of your way so you can torque on the nut. However, don't jack it up until the front wheel lifts off the ground. This will tend to pull the shock out of the tube and put all the spring force upward on that nut, and it may seem tight when it really isn't. If the shop had the car on a hoist with the wheels dangling, they might not have caught this.
That might not be the problem anyway.
Check the tie rod ends carefully (inner and outer - squeeze or remove the bellows when you check those), the steering gear preload, and wheel bearings. Yes, they should have been checked out, but even good mechanics (when you can find one) have bad days.
As for the rear, the infamous bushings have already been mentioned. I just changed mine after 183,000km (114,000miles), and they were long overdue. I stuck with the factory bushings, but some folks on this board have been very happy with the IPD replacements.
If those are the original shocks, after 100,000 and 11 years, I think they're probably at the end of their life expectancy. If they aren't original then this could simply be just another commision-grabbing sales pitch - so typical of the swap-till-you-drop mentality of the auto repair industry - and your knock will still be there even with the new struts.
BTW - if you do decide to get shocks, don't even consider Monroe Sensa-Tracs for your Volvo. Those are the worst pieces of shit I've ever used, and really regret ever wasting money on them. Monbloe should stick to bloated American cars that ride like a semi-inflated air mattress in a Perfect Storm. (Can you 'Sensa' I'm not very happy with them?) Anyway, next time I'll get Boge or (if I get a really big bonu$) Bilsteins. I'm not really sure what the factory shocks were, but I'd buy a set from Volvo at inflated prices before I ever bought Monbloes again.
Heck, you might just be getting a knocking from inside the windshield washer tank when it sloshes around. You get used to that eventually :)
So turn up the tunes on that factory CR-712 radio - assuming the speakers don't cut out from time to time, but that's for another post - and enjoy the ride.
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