Upstairs Tenant Purposely Making Noise During Showings

I need advice! I own a upstairs/downstairs duplex in Denver, purchased in October. The upstairs rented out quickly in November and we have a 6-month lease with those tenants through May 31. The downstairs, it's a garden-level, needed renovation. We finished updates in December, and placed the downstairs on the market for rent.

We've haven't had any luck finding tenants until we recently lowered the unit to a price point that meets the market. Since then, we've had a number of showings. Probably 20 in the last 2 weeks. Whenever the tenants upstairs are there, which is often as one doesn't have a job, they stomp around the unit. It's only 826 sq ft. 

At first, we thought it was an older house with little soundproofing, BUT today we watched the upstairs tenants leave the house, notice people were walking into the downstairs to view the unit, and walk back into the house to stomp around for 10 minutes and then leave again. I'm 100% positive they are doing this purposely to deter anyone from moving in below. 

Our lease with the upstairs tenants ends in May, and we will not renew with these tenants. However, what are we supposed to do in the meantime? Continue to show the unit and hope for the best? 

We used a BiggerPockets lease agreement, which contains the following under Use of Premise: 

Tenant agrees to limit use of the Premises to those uses consistent with the Premises’ clean, safe, sanitary, and habitable condition. Neither Tenant nor Tenant’s licensees or invitees shall be a nuisance or act in any manner that would interfere with the quiet enjoyment by adjacent property owners. This prohibition includes, but is not limited to, loud noises, loud music, noxious or unpleasant odors, and disruptive behavior or actions.

Advice PLEASE!