Diverticulitis: Given the patient's age and the nature of the pain, diverticulitis is a common condition that could present with RLQ pain and a sensation of tightness or a knot, especially if the diverticula are located in the sigmoid colon which can sometimes refer pain to the RLQ due to the complexity of visceral innervation.

Appendicitis: Although more common in younger populations, appendicitis can occur at any age and may present with atypical symptoms in the elderly, including RLQ pain and a feeling of tightness or a knot.
Intestinal Obstruction: This condition can cause severe abdominal pain, including in the RLQ, and a sensation of tightness due to the buildup of intestinal contents.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic or acute abdominal pain, including in the RLQ, and might be associated with a feeling of tightness.

Ectopic Abdominal Aortic Aneurysm (AAA): Although less common, an AAA can present with abdominal pain and should be considered, especially in older patients with risk factors for vascular disease.
Mesenteric Ischemia: This is a life-threatening condition that requires prompt diagnosis and treatment. It can present with severe abdominal pain out of proportion to physical examination findings.
Ovarian Torsion: Though more common in younger women, ovarian torsion can occur in postmenopausal women, especially if there are ovarian masses, and can present with acute abdominal pain.

Carcinoid Syndrome: This can cause abdominal pain, including in the RLQ, due to a tumor in the small intestine, but it's less common and usually associated with other symptoms like flushing and diarrhea.
Malrotation with Volvulus: Although typically a condition of infancy, it can rarely present in adults with chronic or intermittent symptoms, including RLQ pain.
Intra-abdominal Lymphoma: Can cause abdominal pain and masses, but it's less common and usually part of a systemic disease presentation.