Strange sound from my SX4's brake caliper

Ok, here is a strange sound problem. It is a bit difficult to explain but I will try my best! I have an SX4 which has run about 45k kms. I have tried to maintain my car well and as a result I have not spent on anything major mechanically over the past 3.5 years. Over the past few months, there is distinct "clunking" [or 'clanking' if you would like] from the left front end while driving over short, small undulations on the road. Now here are the characteristics of the sound and occurance: 1. The sound is audible when the car is driven over short small undulations at normal city speed. When I say short small undulations, I am looking at for example, the small hardened lumps formed by melting / flowing tar on otherwise straight smooth roads. 2. The sound does not occur when I drive over the same set of undulations while braking - that is there is no sound when the brake pedal is depressed and driven over the same patch. 3. The sound resembles two thick metal plates making contact continuously - like your typical circular plate weights used for exercising making contact. Can you imagine the sound? [it is about 2-4 clunks per second depending on vehicle speed] 4. There is no sound [or barely any sound] when I drive slowly over real bad patches or on kuchcha roads which involves significant suspension travel. 5. Basically the sound is audible only when driven at normal speed on patches which induce short quick vibrations. I hope I have explained it well enough!! Now, coming to what I have done to have this sorted out. 1. We changed the caliper pin - no result. 2. The OE brake pads were in bad shape, though they could be the culprits. Changed them. Nope - no change. The MGP OE pads replacement are quite bad and therefore I recently installed HAWK pads. The braking has improved significantly but the sound persists. 3. We also dont think it is the suspension. Based on the description above, we have narrowed it down to the caliper being the culprit. Luckily the owner of the garage I take it to also has an SX4 [the Chennai folks will know who] - so, we plan to swap calipers and see if the sound persists. What do you guys think? Anything else that could be the reason?

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