A 42-year-old man presents with a persistent dry cough for 8 weeks. He denies haemoptysis, weight loss, or fever. He has a history of gastro-oesophageal reflux disease (GORD) treated with Omeprazole. He started Ramipril for hypertension 3 months ago. Chest examination is normal. Chest X-ray is unremarkable. What is the most likely cause of his cough?