Please tell me what are some possible causes for stridor in adults?

Not common: Adult really don't tend to have stridor commonly. I would take it seriously if you really have it. Issues such as infection, vocal cord paralysis, scarring of the voice box region, cysts or polyps of the voice box, tumors- benign (respiratory papilloma) or cancerous can cause stridor. Needs to be checked by an ENT asap. Good luck.

Some causes: Acute: Airway trauma, laryngitis usually viral, shock or anaphylaxis, aspiration of foreign body, epiglottitis, and inhalation of smoke or noxious materials. Chronic: Laryngeal tumor, chronic infection and granulomatous disease TB, Wegener's, rheumatoid arthritis, extrinsic tumors pressing on airway, chronic intubation.