Sometimes. Sounds like a card in a bike wheel.

What could that be?

 

When you are accelerating, going up hill, or pushing the engine, you may hear the rotor scrape the underside of the cap if you have a worn distributor gear.

 

If it is coming from under the dash, not in the suspension, it is probably a twig in the HVAC blower. When you turn the blower on for AC/heater , the spinning blades of the blower are hitting the debris. Gain access to the blower housing and clean out the trash. Do a search on getting access to the blower. On most cars, it is from under the dash. On the Blazer, it seems that it is from under the hood on the pass. side. Some have an access panel you unbolt. Then some like mine you actually have to cut along the dotted lines to get access to this area! You need a Factory Service manual for your year make and model. Or do a search for Christine's write up with photo's on the former type with removable panel.