We had a madly infuriating and intermittent squeak from the front OS which started the day after we got the car! Turned out to be a bad shock absorber. It passed the bounce test & was ok around town but was very skittery on surface changes at motorway speeds.
As you said, your problem could just be coincidence but it might be that the change to the alignment has slightly altered the loadings within the suspension, which possibly translates into a squeak in a 9 year old bush.
As to tracking it down, that's tricky. If it was really bad it would have been spotted on a MOT. A mechanic would probably take a pry bar to each joint where there is a bush looking for excess movement or wear. You could consider squirting a bit of silicon on every bush to see if that temporally fixes it.
As an aside we also get the quiet groan at low speeds on uneven surfaces. You have to listen for it with the radio off & the top down but I try hard not to obsess about it.