What is the best way to install an over the range microwave in a Townhouse that has metal wall studs where stove is located? Just by knocking on the wall, I dont hear any wooden studs behind the stove.
Don't knock on the wall too much - your neighbors will call the HOA on you.
Use a stud finder. The new generation finders are much more responsive and accurate than earlier models, so get yourself one and locate the studs you need.
How do you know you have metal studs? I don't think your studs are metal, I think there are wood.
Much of the newer low-cost construction has gone to metal studs for interior non-load bearing walls, and in many places, multi-family residences must now be of non-combustible framing by code. If they are metal studs, a really strong magnet will stick to the wall in a vertical line along the entire stud. It will only stick to nails and screws holding the drywall with a wood stud. If it's a metal stud wall, you've got a lot of demo and finishing work to do before it will support this microwave. It cannot simply be screwed to metal studs like is done with wood studs. You have to install wide solid blocking between the studs where it will mount; 2X12 is the usual, and preferably to the next stud on either side as well. This will stiffen the studs enough to prevent deflection and give you a suitable backing to screw the microwave mount into. Don't attempt to circumvent this by getting a top-hung microwave unless you know that the cabinetry was hung on similar blocking or the whole thing may come down on you. And if the codes require non-com framing, that blocking will have to be non-combustible wood which has to be ordered from the mill by the lumberyard and will take around a month to be delivered. It ain't cheap either. Sometimes the inspectors will allow combustible blocking, sometimes not. You need to know this before starting the project. You'll also need a contractor who is conversant with metal stud construction; most current residential framers are not so you may have to seek a commercial contractor for this job.
Other than for fire code compliance, metal studs are used only because they are cheaper and faster to work with. They are inferior to wood for house framing purposes. Expect them to become the norm for interior walls in new homes, especially "Spec" homes, because the trend is already started and it's growing fast.
While metal studs are a possibility I haven't seen them much in residential construction. However if the wall is a party wall it is a fire rated wall and tearing into it shouldn't be done. If rated it likely has at least two layers of drywall and tapping on the wall may not find the studs. A strong magnet or magnetic stud finder should make it obvious. I've seen 3/4" plywood used as wall backing, but usually in new construction where a large piece can be used and toggle bolts can secure heavy items. A 2x12 is better for screwing in to.